Here's a fun thought.
Where does wizardry come from? My wife and I have long thought it was something like a recessive Changeling- wizards being later-generation descendants of Scions, and that's part of why they "harden" as they get older, and why using their power starts to constrict their choices.
What if the Grigori fathered wizardry? In that case, Mac is watching over his descendants.
Could be. Wizards tend to run in families - Eb-Harry, Charity-Molly, Luccio has been checking on hers. The Knights appear, at least yet, to be descendants of kings - Charlemagne (Michael), Saladin (Sanya), Shiro from the last king of Okinawa (Sho Tai? ). Harry was working that line of thought at one time.
In Simon Hawke's Wizard books all wizards are descended not from angels, but a supernatural race of Old Ones who subjugated humans, warred amongst themselves, and the humans all but wiped them out. Some went native and interbred - if you are a wizard you have some Old One lineage. Not near as intricate as the Dresden series, though.